Chemical Equations &
Reactions
Chapter 8
Objectives




List observations that suggest that a
chemical reaction has taken place.
List three requirements for a correctly
written chemical equation.
Write a word equation and a formula
equation for a given chemical reaction.
Balance a formula equation by inspection.
Chemical Reaction
Process by which one or more
substances are changed into one or more
different substances
Indications of a Chemical Reaction
1.
Evolution of heat & light
Indications of a Chemical Reaction
2.
Production of a gas
Indications of a Chemical Reaction
3.
Formation of a precipitate
Precipitate
A solid that is produced as a result of a
chemical reaction in solution & that
separates from the solution
Indications of a chemical reaction
4.
Change in color. (sumac leaves change
color when chlorophyll is destroyed)
Chemical Equation
Representation, with symbols and
formulas, of the identities and relative
amounts of the reactants and products in
a chemical reaction
Reactants  Products
Follows the Law of Conservation of Mass
Characteristics of Chemical Equations
The equation must represent known facts
The equation must contain the correct
formulas for the reactants & products
The law of conservation of mass must be
satisfied- which means the same # and
type of atoms are present on both sides of
the equation.
Writing Chemical Equations
Word Equation
Represents facts- only qualitative
Example:
Methane + oxygen  carbon dioxide + water
Writing Chemical Equations
Formula Equation
Example:
CH4(g) + O2(g)  CO2(g) + H2O(g)
(not balanced)
Symbols you will see in equations pg.266
Writing Chemical Equations
Balanced Formula Equation
Inserting Coefficients-small whole # that
appears in front of a formula
Multiplies number of atoms of each
element indicated in chemical formula
Example:
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Balancing Chemical Equations
Balance the formula equation according to the
law of conservation of mass



Balance the different types of atoms one at a
time
Balance polyatomic ions that appear on both
sides of the equation as single units
Balance H atoms and O atoms after atoms of
all other elements have been balanced
Examples
Mg + HCl  MgCl2 + H2
Al2(SO4)3 + Ca(OH)2  Al(OH)3 + CaSO4
MgI2 + KNO3  KI + Mg(NO3)2
Writing and Balancing Equations from Word
Equations
1. Write out correct chemical formulas and
symbols.
2. Balance equation.
Solid aluminum metal combines with oxygen
gas to produce solid aluminum oxide
Writing equations from word equations
Examples to try.

1.
Solid calcium metal reacts with water to form
aqueous calcium hydroxide and hydrogen gas.
2.
Solid iron(III)oxide and carbon monoxide gas
produces solid iron and carbon dioxide gas.
3.
Solid copper reacts with aqueous silver nitrate to
produce aqueous copper (II) nitrate and solid
silver.
Objectives



Define & give general equations for
synthesis, decomposition, singlereplacement, and double-replacement
reactions.
Classify a reaction as synthesis,
decomposition, single displacement,
double displacement or combustion.
Predict the products of simple reactions if
given the reactants.
5 Basic Types of Reactions





Synthesis
Decomposition
Single-replacement
Double-replacement
Combustion
Synthesis Reactions

A reaction in which two or more
substances combine to form a new
compound
A + X  AX
A and X are elements or compounds
AX is a compound
Synthesis Reactions

Examples:
magnesium + oxygen  __________
iron + oxygen  __________
calcium oxide + water  __________
Decomposition Reactions


A reaction in which a single compound
produces two or more simpler substances
Opposite of synthesis reactions
AX  A + X
AX is a compound
A and X are elements or compounds
Decomposition Reactions
(Binary Compounds)

Decomposition of a binary compound into
its elements.

Example:
water  __________ + __________
Electrolysis
The decomposition of a substance by an
electric current
Decomposition Reactions
(Metal Carbonates)

Metal carbonates decompose to produce a
metal oxide & carbon dioxide gas.

Example:
calcium carbonate  ______ + ______
Decomposition Reactions
(Metal Hydroxides)

Metal hydroxides (except group 1 metals)
decompose to produce metal oxides &
water.

Example:
calcium hydroxide  ______ + ______
Single-Replacement Reactions



A reaction in which one element replaces
a similar element in a compound
A + BX  AX + B
- or –
Y + BX  BY + X
A, B, X, Y are elements
AX, BX, BY are compounds
Single-Replacement Reactions
(Replacement of a Metal or Nonmetal)

Example:
aluminum + lead nitrate  ____ + ____
fluorine + sodium chloride  ____ + ____
Double-Replacement Reactions
A reaction in which the ions of two
compounds exchange places in an
aqueous solution to form two new
compounds


AX + BY  AY + BX
A, X, B, Y in reactants represent ions
AY & BX represent ionic or molecular
compounds
Double-Replacement Reactions
(Formation of a Precipitate)

One cation of one reactant combine with the
anions of another reactant to form insoluble
or slightly soluble compound

Example:
Potassium iodide + lead (II) nitrate 
____ + ____
Double-Replacement Reactions
(Formation of a Gas)

Example:
Iron(II) sulfide + hydrochloric acid 
____ + ____
Double-Replacement Reactions
(Formation of Water)

Example:
hydrochloric acid + sodium hydroxide 
____ + ____
Combustion Reactions
A reaction in which a substance combines
with oxygen, releasing a large amount of
energy in the form of light and heat
Combustion of a hydrocarbon always
yield carbon dioxide and water.
Combustion Reactions

Example:
propane + oxygen  ____ + ____
(C3H8)
Try this:

Write a balanced chemical equation for the
following reaction:
Ethyl alcohol (C2H5OH) burns to produce
carbon dioxide and water.
Objectives


Explain the significance of an activity
series.
Use an activity series to predict whether a
given reaction will occur and what the
products will be.
Activity Series


A list of elements organized according to
the ease with which the elements undergo
certain chemical reactions
Used to help predict whether certain
chemical reactions will occur
Activity Series




Table 8.3, p. 286
An element can replace any element
below it but not above it
Based on experiment
Will be given to you on test.
Examples





Using the activity series, predict whether
each of the possible reactions will occur.
For the reactions that will occur, write the
products & balance the equation.
Ba(s) + H2O(l) 
Cu(s) + HBr(aq) 
Al(s) + HBr(aq) 
F2(g) + NaCl(s) 